Characterising biochemical reaction network structure in mathematical terms enables the inference of functional biochemical consequences from network structure with existing mathematical techniques... Show moreCharacterising biochemical reaction network structure in mathematical terms enables the inference of functional biochemical consequences from network structure with existing mathematical techniques and spurs the development of new mathematics that exploits the peculiarities of biochemical network structure. The structure of a biochemical network may be specified by reaction stoichiometry, that is, the relative quantities of each molecule produced and consumed in each reaction of the network. A biochemical network may also be specified at a higher level of resolution in terms of the internal structure of each molecule and how molecular structures are transformed by each reaction in a network. The stoichiometry for a set of reactions can be compiled into a stoichiometric matrix N is an element of Z(mxn), where each row corresponds to a molecule and each column corresponds to a reaction. We demonstrate that a stoichiometric matrix may be split into the sum of m - rank(N) moiety transition matrices, each of which corresponds to a subnetwork accessible to a structurally identifiable conserved moiety. The existence of this moiety matrix splitting is a property that distinguishes a stoichiometric matrix from an arbitrary rectangular matrix. (C) 2020 Elsevier Ltd. All rights reserved. Show less
Reil, J.C.; Reil, G.H.; Kovacs, A.; Sequeira, V.; Waddingham, M.T.; Lodi, M.; ... ; Hamdani, N. 2020
Key pointsThe Anrep effect represents the alteration of left ventricular (LV) contractility to acutely enhanced afterload in a few seconds, thereby preserving stroke volume (SV) at constant preload... Show moreKey pointsThe Anrep effect represents the alteration of left ventricular (LV) contractility to acutely enhanced afterload in a few seconds, thereby preserving stroke volume (SV) at constant preload. As a result of the missing preload stretch in our model, the Anrep effect differs from the slow force response and has a different mechanism. The Anrep effect demonstrated two different phases. First, the sudden increased afterload was momentary equilibrated by the enhanced LV contractility as a result of higher power strokes of strongly-bound myosin cross-bridges. Second, the slightly delayed recovery of SV is perhaps dependent on Ca2+/calmodulin-dependent protein kinase II activation caused by oxidation and myofilament phosphorylation (cardiac myosin-binding protein-C, myosin light chain 2), maximizing the recruitment of available strongly-bound myosin cross-bridges. Short-lived oxidative stress might present a new facet of subcellular signalling with respect to cardiovascular regulation. Relevance for human physiology was demonstrated by echocardiography disclosing the Anrep effect in humans during handgrip exercise. The present study investigated whether oxidative stress and Ca2+/calmodulin-dependent protein kinase II (CaMKII) activity are involved in triggering the Anrep effect. LV pressure-volume (PV) analyses of isolated, preload controlled working hearts were performed at two afterload levels (60 and 100 mmHg) in C57BL/6N wild-type (WT) and CaMKII-double knockout mice (DKOCaMKII). In snap-frozen WT hearts, force-pCa relationship, H(2)O(2)generation, CaMKII oxidation and phosphorylation of myofilament and Ca(2+)handling proteins were assessed. Acutely raised afterload showed significantly increased wall stress, H(2)O(2)generation and LV contractility in the PV diagram with an initial decrease and recovery of stroke volume, whereas end-diastolic pressure and volume, as well as heart rate, remained constant. Afterload induced increase in LV contractility was blunted in DKOCaMKII-hearts. Force development of single WT cardiomyocytes was greater with elevated afterload at submaximal Ca(2+)concentration and associated with increases in CaMKII oxidation and phosphorylation of cardiac-myosin binding protein-C, myosin light chain and Ca(2+)handling proteins. CaMKII activity is involved in the regulation of the Anrep effect and associates with stimulation of oxidative stress, presumably starting a cascade of CaMKII oxidation with downstream phosphorylation of myofilament and Ca(2+)handling proteins. These mechanisms improve LV inotropy and preserve stroke volume within few seconds. Show less
